Znorg. Chem. 1983, 22, 181 either the five-coordinate Fe(II1) in C1Fe(Etzdtc)z16(0.50 mm/s, 100 K vs. Fe) or the five-coordinate Fe(I1) in the [Fe(Et2dtc)JZ dime;16 (0.90 mm/s, 100 K vs Fe). The voltammetry of’I in B M F ” shows both a reduction wave at -1.2 V and an oxidation wave at -0.07 V. Quantitative studies of these waves by chronoamperometry show both the oxidation and the reduction to be diffusion controlled over the range of 20 ms-1 s. The current functions i,t’/2/Cand i,t‘lz/C for the reduction and oxidation, respectively, correspond to one-electron processes. The reduction wave shows no associated anodic wave, and the reduction product appears completely unstable. The oxidation wave is accompanied by a small cathodic wave. The ic/iaratio in double potential step chronoamperometry shows the oxidation product to be stable for about 100 ms. A significant decline in this ratio is observed at longer potential steps ( i J i , = 0.16, t = 1 s). The [ Fe4S4L4]2- clusters generally undergo reversible oneelectron reductions. The apparently different redox properties of I must be attributed mainly to the Etzdtc- ligand. The latter is known to stabilize highly oxidized states in simple M(Etzdtc), c0mp1exes.l~ The effects of terminal ligand coordination characteristics in the redox properties of the [Fe4S4L4In-clusters at present are not well understood. A systematic study of the molecular and electronic structures and redox properties of various “mixed” terminal ligand clusters is under way in our laboratory. Acknowledgment. This research was supported by a grant from the National Institutes of Health (No. GM-26671-03). X-ray equipment used in this research was obtained in part by Grant CHE-8 109065 from the National Science Foundation. Registry No. I, 83692-59-5; (Ph4P)2[Fe4S4(SPh)2Clz], 80939-30-6; (Ph4P)J Fe4S4(SPh),], 80765-13-5. Supplementary Material Available: Tables of structure factors and positional and thermal parameters (26 pages). Ordering information is given on any current masthead page. (16) De Vries, J. L. K. F.; Keijzers, C. P.; De Boer,E. Znorg. Chem. 1972, 11, 1343. (17) The electrochemical studies were conducted in DMF solution (0.1 M) in n-Bu4NC104on a Pt electrode vs. a saturated calomel reference electrode. (18) Johnson,C. K. Report ORNL-3794; Oak Ridge National Laboratory: Oak Ridge, TN, 1965.
Department of Chemistry University of Iowa Iowa City, Iowa 52242
M. G. Kanatzidis M. Ryan D. Coucouvanis*
Nuclear Research Center “Demokritos” Aghia Paraskevi, Attiki, Greece
A. Simopoulos A. Kostikas
Received August 2, 1982
Spontaneous Carbon-Carbon Bond Cleavage of Some Ruthenium(I1)-Bound a-Substituted Ketoximes
Sir: We report the first example of C-C bond cleavage in a ligand attached to ruthenium(I1) that is not accompanied by an oxidation-reduction reaction.’ The reaction, which occurs when (H3N)5R~OH2z+ is generatedZin the presence of a ketoxime containing an a-keto or
+
(1) Ru(NH3j5N03+ a-methylene ketones: K. Schug and C. P. Guengerich, J . Am. Chem. Soc., 101, 235-6 (1979). Other types of
enhanced ligand reactivity also are accompanied by net redox changes.
181
a-hydroxy group, has the overall stoichiometry C,H3 ( H ~ N ) ~ R ~ ( O H J +t
HON =C
R‘ ( H ~ N ) ~ R u - N G C - C H ~ 7.t
t
R-OH
(1)
where R is -C(O)CH3, -C(O)C6Hs, or -CH(OH)C&,. The ruthenium(I1)-nitrile products were isolated as the perchlorate salts and identified by comparison of their UV-vis and IR spectra with those of authentic samples3 Benzoic acid was recovered and identified (proton NMR and IR spectra and melting point) in the R = C(0)C6HScase, and benzaldehyde was identified (proton NMR) in the R = CH(OH)C6H5 case. Since these oximes do not normally decompose in aqueous solutions and ligand substitution for HzO in (H3N)5R~-OH22+ is rapid,4 the reaction must involve the two steps shown in eq 2.
L
I
R-OH
(2b)
Attempts to isolate or detect the presence of the proposed ruthenium(I1)-oxime intermediate, I, were unsuccessful, suggesting that the rate of disappearance of I is fast compared to its rate of formation. This remarkable increase in the reactivity of the oxime ligand in the absence of a concurrent redox change provides unambiguous evidence for the ability of Ru(I1) to promote increased unsaturation on bonded nitrogen atoms, a phenomenon generally attributed to strong back-bonding from the filled 4d orbitals on Ru(I1) to the empty a* orbitals on sp2- or sp-hybridized nitrogen5 Reactions were carried out at about 25 ‘C in dilute solution (-0.01 M in Ru and -0.02 M in oxime). A lower limit of 0.020 s-l can be estimated for kb if it is assumed (a) that [I] < [RutOtal]/lO,(b) that k, is similar to that for other sp2-hybridizedligands4(average of seven neutral unhindered ligands 0.10 M-’ s-l, range 0.05-0.20 M-’ s-l), and (c) that reaction 2b is first order. Related studies on aldoximes and unsubstituted oximes will be reported elsewhere. Acknowledgment. This research was supported in part by the Metal Loan Program of Johnson Matthey, Inc. Registry No. (H3N)5R~(OH2)2+, 21393-88-4; HON=C(CH3)C(O)CH3, 57-71-6; HON=C(CH,)C(O)C,H,, 119-51-7; HONE C(CH3)CH(OH)C6H5,26226-58-4; (H3N)5R~N=CCH32+, 2654031-8; HOAc, 64-19-7; benzoic acid, 65-85-0; benzaldehyde, 100-52-7. (H3N)RuOHz2+(aq)is prepared from [(H3N),RuCI]C12(A. D. Allen and C. V. Senoff, Can. J. Chem., 45, 1337 (1967)) by treatment with Ag+(aq) or OH-(aq) followed by amalgamated zinc. (3) P. C. Ford and R. E. Clarke, Znorg. Chem., 9, 227-35 (1970). (4) R. E. Sheperd and H. Taube, Znorg. Chem., 12, 1392-401 (1973). ( 5 ) (a) P. C. Ford, Coord. Chem. Rev., 5, 77-99 (1970); (b) H. Taube, Sum. Prog. Chem., 6 , 1-46 (1973).
Department of Chemistry Illinois Institute of Technology Chicago, Illinois 606 16
Charles P. Guengerich Kenneth Schug*
Received September 16, 1982
0020-1669/83/ 1322-0181$01.50/0 0 1983 American Chemical Society
